This code is really awful to understand, because it's really messy.

• Tab and space your code correctly -- it's impossible to see how it's grouped
• Use good variable names -- it's impossible to guess what most of the functions and variables are supposed to do.

There are some serious mistakes easily visible:

• plrv isn't defined
• swapping is a global variable
• DrawDBRay is defined twice
• The entire program is inside the PlayerAdded event

You have ~a dozen local variables for each player... but that much state is complicated and likely unnecessary (they're essentially unnamed, so it's hard to tell). This makes it hard to separate a lot of the functions. However, it's still possible. DrawDBRay, upd.OnServerEvent can be pulled out.

You can use workspace instead of game.Workspace.

Use while not x do wait() end instead of if not x then repeat wait() until x end.

Don't repeat yourself! If the only thing that's different is one number... then only change that number, with a variable!

Don't use if a then elseif not a then. Just use if a then else.

You can use FindPartOnRay's ignore for the Character instead of just GetChildren()ing a model and using FindPartOnRayWithIgnoreList.

You use player.Character repeatedly despite having a pm variable -- maybe name that character instead??

Define functions to do things -- you repeat a block of code to damage a part that you hit 4 times instead of just defining a function. Something like this:

-- Deals damage to a descendant of a character.
-- A character has a Humanoid and a Team IntValue.
-- Dealing damage to something named "Head" doubles "damage"
function dealDamage(model, attackerTeam, damage)
    if not model then
        return -- Didn't hit anything
    end
    if model:FindFirstChild("Humanoid") then
        local team = workspace[model.Name].Team.Value
        if team ~= attackerTeam then
            model.Humanoid:TakeDamage(damage)
        end
        return
    end
    -- Double damage for headshots
    if model.Name == "Head" then
        damage = damage * 2
    end
    -- Try the parent, since there wasn't a humanoid to hit.
    return dealDamage(part.Parent, attackerTeam, damage)
end

Define variables in the narrowest scope possible. Your variable barrel is only meaningfully used in fire.OnServerEvent, yet it's defined 200 lines earlier. costume, the same.

No point to check for something to exist and then wait for it -- just WaitForChild -- it does that check for you.

There is no "TShirt" class. You didn't name "Shirt". There is a "Clothing" class which covers "Pants" and "Shirts". Use or instead of repeating yourself...

Why are you doing this?

w2.C1:lerp(CFrame.new(0, 0, 0) * CFrame.Angles(math.rad(0), 0, 0), 1)

That's the same thing as

CFrame.new()

There's no point in setting all the values to nil when they die, since all of this is redone for each new character anyway.

Big Bug

The behavior you have is caused by reconnecting every one of these events each time the player dies. That's the reason you should avoid these stateful designs.

You only want to act for the currently spawned player. First you should clean up this mess, though.

At this point, Melee.OnServerEvent can be lifted out to an outer scope.

Maybe make a makeWeapon function for the reuse in weldGun.

This is the most sense I could make of this, but there is considerable improvement to be made.

To fix the bug, you have to pull all of the functions out of newCharacter. That requires eliminating all of the variables defined inside it.

The simplest way to do that is to swap it like this:

function newCharacter(plr, character)
    .....

    local blah = x
    .....
    y.connect(function(player)
        print(blah)
    end)

becomes

local dictionary = {}

function newCharacter(plr, character)
    .....
    dictionary[plr] = {}
    dictionary[plr].blah = x
    .....
end

y.connect(function(player)
    print( dictionary[player].blah )
end)